Apoptosis is a morphologically defined process leading to cell death. This event can be induced in cells by radiation, chemotherapeutic agents, or receptor binding of tumor necrosis factor receptor (TNFR) and Fas. In this proposal the involvement of the small GTP binding proteins Rho and Ras and the kinases MEKK and JNK will be examined in receptor induced apoptosis in human cancer cells. Inhibitors of Rho and Ras signaling will be microinjected or inducibly expressed and the effect on apoptosis and MEKK and JNK activation by TNFR and Fas will be assessed. In addition, constitutively active Rho and Ras, individually and in combination, will be examined for their ability to activate MEKK and JNK and induce apoptosis. Demonstration of these signaling pathways downstream of TNFR and Fas will be a novel finding. Elucidation of the signal transduction pathways that lead to apoptosis will have a significant impact on the treatment of cancer and other diseases.